This invention pertains generally to the field of surgical instruments and similar devices, to micromechanical systems, and to ultrasonically actuated instruments.
Various medical procedures require the injection of material into and/or the removal of material from a patient. For example, medication or other life sustaining fluids may be required to be injected either intravenously or subcutaneously into a patient. Blood and/or other fluids may be required to be removed from a patient for, e.g., testing, and/or to relieve fluid pressure within the patient""s body. Sample cells may be required to be removed from, e.g., a tumor, for testing, preferably without requiring highly invasive surgery. Such medical procedures are typically and preferably performed using a surgical device including a hollow needle, or some similar device, with a rigid needle-like structure for passing into tissue and with a fluid flow channel formed therein. For example, a simple hypodermic needle may be used to inject medication into a patient. A hollow needle positioned in a patient may be connected to a fluid supply, such as a bag of saline solution which may, or may not, include additional medications, and an infusion pump employed to pump fluid from the supply through the needle into the patient. More complicated needle-like surgical instruments may be employed to perform more complicated surgical procedures, such as, for example, removing portions of a tumor or other tissue from a patient""s body.
An example of a surgical procedure employing a relatively more complicated needle-like surgical tool is phacoemulsification. Phacoemulsification is the predominant method of removing cataracts (a loss of transparency of the lens of the eye) used throughout the world. Phacoemulsification is a method of emulsifying and aspirating a cataract with a low-frequency ultrasonic needle. An exemplary conventional system 10 for performing phacoemulsification is illustrated in FIG. 1. In such a system 10, a needle-like ultrasonically driven cutting tool 12, with a pointed distal end 14, is provided for cutting and removing a cataract lens. The pointed distal end 14 of the tool 12 penetrates into the eye chamber 16 so as to be positioned in contact with the cataract lens 18 to be cut and removed. The ultrasonic cutting tool 12 is driven longitudinally (e.g., at 40-65 kHz) to fragment the cataracts (deteriorated, cloudy eye lenses) with the hollow vibrating distal tip 14 of the cutter 12. A double lumen channel may be formed running axially from an aperture at the distal tip 14 of the cutter 12 to a proximal end 20 thereof. For example, the double lumen channel may be formed as an outer lumen channel 22 with an inner lumen channel 24 formed running through the length of the outer lumen channel 22. During the process of fragmenting the cataract lens 18, irrigation and aspiration are preferably provided simultaneously through the lumens 22 and 24. For example, irrigation may be provided as a saline solution, provided from a bottle or bag of saline 26, through an, e.g., flexible silicone tube 28, and the outer lumen 22 of the cutting tool 12 to the eye chamber 16. Irrigation maintains the interior chamber pressure as material and fluid are removed from the eye chamber 16. Aspiration may be provided, for example, by a peristaltic pump 30 coupled, e.g., by flexible silicone tubing 32, to the inner lumen 24 at the proximal end 20 of the ultrasonic cutter 12. Operation of the pump 30 is controlled by a control circuit 34. Aspiration serves two purposes. It removes the fragments broken from the cataract lens 18 by longitudinal vibration of the ultrasonic cutter tip 14, and it holds lens particles against the ultrasonic tip 14 to allow efficient fragmentation by pre-stressing the tissue.
Constant pressure monitoring and fluidics control are especially important during aspiration in the phacoemulsification process. If the aperture at the tip 14 of the ultrasonic cutter 12 becomes occluded with tissue fragments, vacuum levels could rise to excessive levels. A sudden release of the occlusion may result in a pressure pulse, which can collapse the anterior chamber 16 of the eye. Thus, it is important to provide feedback to the control circuit 34 of pressure changes in the lumen 24 through which aspiration is performed. In a conventional phacoemulsification system 10, pressure feedback is provided by a pressure sensor 36 located in a control unit, near the control circuit 34 and peristaltic pump 30, but removed from the ultrasonic cutter 12. The pressure sensor 36 is coupled to the ultrasonic cutter 12 via the compliant silicone tubing 32 which couples the pump 30 to the tool. The length of the tubing separating the pressure sensor 36 from the ultrasonic cutter 12 creates a time delay between pressure changes occurring at the tip 14 of the ultrasonic cutter 12 and the detection of such pressure changes by the pressure sensor 36. This time delay, especially resulting from occlusion of the aperture in the cutting tool tip 14, between eye pressure transients and the measured pressure, can cause improper feedback control of the pump, with clinically deleterious effects. In addition to the time delay, the silicone tubing 32 connecting the pressure sensor 36 to the ultrasonic cutter 12 can collapse, causing at least temporary complete loss of pressure feedback. Pressure loss along the tubing 32 can also result in inaccurate pressure feedback measurements. What is desired, therefore, is a reliable system and method for measuring pressure and flow changes in, for example, a needle ultrasonic surgical cutter tool employed as part of a phacoemulsification system, and similar needle-like surgical tools employed for injecting fluids into and removing materials from a patient.
Ultrasonically driven surgical tools, and needle-like surgical tools in general, are conventionally manufactured from appropriate metal materials, such as titanium (for ultrasonic tools) or surgical steel. However, it has been determined that such surgical tools may, advantageously, be implemented as micromachined silicon structures. Such silicon surgical tools may be manufactured to have high strength and sharper cutting tips than similar metal tools, thereby providing for easier cutting. Such tools may be manufactured using conventional low-cost micro-mechanical mass (batch processing) fabrication techniques, which makes such tools low-cost and disposable. Micromachined silicon surgical tools also have the advantage of higher maximum achievable stroke velocity and lower heat generation, due to the high thermal conductivity of silicon, thereby resulting in less tissue damage due to friction induced heating of the tool. Furthermore, sensors and control circuits may be integrated directly onto surgical tools fabricated from silicon using conventional micro-mechanical processing techniques, thereby enabling effective closed circuit control of tool operation. Examples of micromachined silicon ultrasonic needle-like surgical tools include the ultrasonically actuated needle pump system described in U.S. patent application Ser. No. 09/617,478, filed Jul. 17, 2000, by Amit Lal, et al., as well as the vibrationally actuated cutting instrument described in U.S. patent application Ser. No. 09/605,323, filed Jun. 28, 2000, by Amit Lal, et al. The latter describes, for example, a strain sensor integrated onto a silicon vibrationally activated cutting tool to provide an output signal that may be used in a feedback loop to control operation of the tool. For example, a signal provided by the strain sensor mounted near the tip of such a tool may be used as a feedback signal to a feedback controller for controlling an electrical power driver that is connected to supply oscillating power to the tool, so as to maintain the amplitude of the vibrations at a selected level to control, e.g., the cutting and pumping rate of the tool.
The present invention provides a needle-like surgical tool with an integrated pressure and/or flow sensor thereon. The integrated sensor is coupled directly to a fluid flow channel formed in the surgical tool, through which fluid may be injected into or drawn from a patient using the tool. The sensor is thus able to provide an electrical signal which is immediately responsive to changes in conditions (pressure or flow) in the fluid flow channel. Such electrical signals provided by the sensor may be employed in a feedback loop to control, e.g., a peristaltic pump, or other device, which is coupled to the tool fluid flow channel, thereby to control accurately the pressure and/or flow in the channel. Surgical tools with integrated pressure and/or flow sensors in accordance with the present invention may include, for example, needle-like surgical tools which are employed generically for injecting fluids into or extracting material from a patient, or more sophisticated surgical tools, such as ultrasonically actuated cutting instruments used, for example, in a phacoemulsification system.
A surgical tool with integrated pressure and/or flow sensors in accordance with the present invention may be implemented, for example, as a micromachined silicon device, with integrated pressure and/or flow sensors formed thereon using conventional low-cost mass fabrication processing techniques. For example, a silicon needle with integrated pressure and/or flow sensors in accordance with the present invention may be formed by etching two half needles, with grooves formed along the length of each half needle, out of a silicon wafer using conventional processing techniques. The two half needles are bonded together such that the grooves formed therein form a channel inside the needle through which a fluid may flow. A further etch opening on the backside of one of the half-needles, in fluid communication with the fluid flow channel, results in a thin (silicon nitride) membrane formed as a pressure sensing component in the pathway of the needle channel. Resistors are formed on the membrane (and, preferably, on the rigid surface of the silicon tool nearby), e.g., by depositing a thin polysilicon (LPCVD) film on the membrane, implanting the film with a dopant such as boron, and then patterning the doped polysilicon film into a resistor pattern. Conductors, e.g., aluminum lines, may be formed (e.g., by sputtering) onto the tool, to connect the resistors formed over (and near) the membrane into a circuit configuration (e.g., a Wheatstone bridge circuit), and with connector pads, e.g., also of aluminum, formed on the tool. Wires may be employed to connect the resistor circuit via the connector pads to a supply/amplifier circuit, e.g., provided on packaging to which the tool is bonded.
Load pressure in the surgical tool fluid/flow channel generates stress in the membrane with the resistors formed thereon. This stress results in a change in resistance of the resistors formed over the membrane. Changes in the resistance of the resistors formed over the membrane may be detected essentially instantaneously in response to changes in pressure in the surgical tool fluid flow channel. Thus, the pressure sensor formed by the resistors formed on the membrane may be used to generate a highly responsive feedback signal which may, in turn, be used to control a peristaltic pump, or other device, to control the pressure in the surgical tool fluid flow channel and, therefore, in the area adjacent to the channel aperture formed at the distal end of the tool. Thus, for example, where the present invention is employed with an ultrasonically actuated cutting tool employed for phacoemulsification, the feedback signal provided by a pressure sensor integrally formed on the tool may be employed to provide proper feedback control in response, for example, to occlusion of the cutting needle tip, thereby to prevent damage to the eye chamber in the event of such an occurrence during aspiration of the fragments of an emulsified cataract lens.
A sensor integrally formed on a silicon surgical tool in accordance with the present invention may also be employed to detect other related conditions in the fluid flow channel of the tool. For example, the sensor can also be used to sense fluid flow. Fluid flow in the fluid flow channel modifies the heat transfer from the resistors formed on the membrane. The resistance change due to flow can be sensed and used as a feedback signal. Under free flow conditions the output signal produced by the integral sensor can result from both flow and pressure effects. Thus, both flow and pressure signals can be obtained from such a sensor.
As mentioned above, the present invention may be employed in a micromachined silicon surgical cutting tool for phacoemulsification. Such a tool will have ultrasonic activators bonded thereto for ultrasonically driving the tool. The tool may be formed in a horn shape (e.g., a catenary horn) for focusing ultrasonic energy at the cutting tip of the tool. A pressure/flow sensor in accordance with the present invention is preferably integrally formed near the end of the tool opposite the cutting tip, to minimize the stress concentration factor thereon. A strain sensor may be formed near the tip of the tool, to provide a signal for feedback control of tool oscillation. The entire micromachined silicon cutting tool in accordance with the present invention may be bonded to packaging (such as an IC DIP package), preferable at a null point or displacement node of the horn/needle structure, to minimize coupling of ultrasonic vibration of the tool to the packaging and any circuitry formed thereon.
Further objects, features, and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings.